1. Field of the Invention
The present invention relates to acetal resin compositions containing a specific component of a multiphase interpolymer. More particularly, it relates to acetal resin compositions exhibiting excellent matte property and flexural modulus, and capable of inhibiting mold deposit in the mold processing.
2. Description of Related Art
An acetal resin has been widely used as an engineering resin in various fields, especially automobile and home electric appliance fields, for its excellent mechanical and molding properties. However, molded products of an acetal resin have a high surface gloss so that sometimes a feeling of quality is harmed when they are used for interior automotive trim. Thus, there is a great need for matte molded products.
To obtain matte molded products, there have been known several methods such as a matte process for molding resins with an embossing mold and a painting process for making matte coatings. The former process cannot provide desirable matte molded procuts, and the latter process unfavorably has environmental problems due to organic solvents contained in the coatings.
Various types of low gloss acetal resin compositions have been developed. Japanese Patent Application Laid-Open Nos. 54053/1989 and 170641/1989 and European Patent Unexamined Publication No. 342,000 disclose compositions incorporating elastomeric polymers or inorganic fillers in a resin matrix. However, the incorporation of the elastomeric polymers for maintaining or improving the impact resistance may have degraded heat resistance. In the latter composition, a sufficient matte effect is not attained though irregular reflection results from a rough surface of the molded product. The additives lower the mechanical properties, especially extensibility and toughness, of the compositions. Moreover, the products molded with such acetal resin compositions have extremely degraded weathering resistance (light stability) so that they are not suitable for use in interior automotive trim.
Acetal resin compositions incorporating a multiphase interpolymer are also known. European Patent Unexamined Publication No. 115,373 discloses high impact resistant thermoplastic acetal molding compositions which are modified with a multiphase interpolymer comprising a cross-linked acrylic central phase and a rigid thermoplastic outermost phase grafted thereon.
U.S. Pat. Nos. 3,749,755 and 4,639,488 disclose molding compositions based on a mixture of an oxymethylene polymer and an elastomeric graft copolymer which exhibit high impact resistance. However, these compositions have considerably degraded mechanical properties, especially, strength and elasticity, which an acetal resin inherently possesses, and their thermal stability during processing are not sufficient. Such compositions are not intended to improve their matte property, therefore, the matte effect is not satisfactory and neither is the weathering resistance.
Japanese Patent Application Laid-Open No. 294352/1990 discloses acetal resin compositions including a multiphase interpolymer and a methacrylate polymer. The compositions are produced only to improve weathering resistance so that their matte property is not improved.
Further, for the purpose of improving weathering resistance (light stability), it is well known that stabilizers such as ultraviolet (referred to hereinafter as UV) absorbers and light stabilizers can be added to acetal resins. However, they do Rot exhibit excellent mold deposit in spite of their good weathering resistance.
As described above, conventional acetal resin compositions do not possess an excellent matte property while retaining good flexural modulus and preventing undesirable mold deposit.